The international envoy to Syria has warned the war in the country is worsening by the day, and that as many as 100,000 people could die in the next year.

Lakhdar Brahimi says dialogue between the government of president Bashar al-Assad and the opposition remains the only way to avoid further bloodshed, but the opposition forces remain adamant that Mr Assad's government cannot be involved in any peace plan.

"The situation in Syria is bad, very, very bad." he said.

"It is getting worse, and worsening more quickly. If about 50,000 people were killed in nearly two years, and the war continues for another year, we won't have 25,000 more dead, we will have 100,000."

When former UN secretary-general Kofi Annan quit the role of envoy in frustration and Mr Brahimi took up the post in August, he said it was an almost impossible task.

Less than five months later the veteran trouble shooter is warning Syria could soon become a failed state ruled by warlords.

Mr Brahimi has been pushing a peace plan drawn up in Geneva in the middle of the year, with the support of Syria's key ally, Russia and the other permanent members of the Security Council.

After a series of meetings in Damascus and then Moscow, he has reported back to the Arab League in Cairo, telling a press conference there is still a chance a plan based on the Geneva agreement could be accepted by the international community and succeed in bringing peace.

"Geneva was a compromise and it's understandable that it has different interpretations," he said.

"But I think Geneva aims at a change that is total and a change that is acceptable to the people of Syria."

The Geneva agreement talks about a transitional government and movement toward elections, but it is silent on the fate of Mr Assad and the opposition is adamant he must have no role.

That is where the diplomacy has been stuck, as the bodies have piled up.

As Mr Brahimi headed to Moscow, there were faint hopes he might be making progress.

Russia has been stepping away from Mr Assad, acknowledging calls for him to go and offering to talk to the Syrian opposition, but Russia has also just reaffirmed that Mr Assad has no intention of stepping down.

And Mr Brahimi acknowledged that neither Mr Assad nor the opposition were willing to talk to each other.

"You know, this is the problem," he said.

"The problem is that both sides are not speaking to one another, are speaking across of one another. And this is where help is needed from outside to make sure that we, everybody speaks about the same thing."